AD7626 Analog Devices, AD7626 Datasheet - Page 18

• Manufacturer Part Number: AD7626
• Description: 16-Bit, 10 MSPS, PulSAR Differential ADC
• Manufacturer: Analog Devices

Specifications of AD7626

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 10MSPS
• Interface: LVDS,Ser
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP

AD7626
DRIVING THE AD7626
Differential Analog Input Source
Figure 33 shows an
to the AD7626.
Single-Ended-to-Differential Driver
For applications using unipolar analog signals, a single-
ended-to-differential driver (as shown in Figure 32) allows
for a differential input into the part. This configuration, when
provided with an input signal of 0 V to 4.096 V, produces a
differential ±4.096 V with midscale at 2.048 V. The one-pole
filter using R = 20 Ω and C = 56 pF provides a corner frequency
of 140 MHz. The VCM output of the AD7626 can be buffered
and then used to provide the required 2.048 V common-mode
voltage.
Single-Ended or Fully Differential High Frequency Driver
In applications that require higher input frequency tones, the
ADA4932-1 can be used to drive the inputs to the AD7626. The
ADA4932-1 is a differential driver, which also allows the user
the option of single-ended-to-differential conversion.
Figure 34 shows the typical circuit for a 50 Ω source impedance
(ac-coupled in this example). The input to the
configured to be balanced to the source impedance (in this case
50 Ω). Further information on balancing the input impedance
to the source impedance can be found on the ADA4932-1
datasheet. The circuit shown in Figure 34 operates with an
overall gain of ~0.5 when the termination input termination
is taken into account.
Alternatively, the ADA4932-1 can be used with a fully diffe-
rential source—it acts as an inverting differential driver.
ADA4899-1
1
2
BUFFERED VCM PIN OUTPUT
GIVES THE REQUIRED 2.048V
COMMON-MODE SUPPLY FOR
ANALOG INPUTS.
SEE THE VOLTAGE REFERENCE OPTIONS SECTION. CONNECTION TO EXTERNAL REFERENCE SIGNALS
C
IS DEPENDENT ON THE EN1 AND EN0 SETTINGS.
DECOUPLE REF AND REFIN PINS AS PER THE EN1 AND EN0 RECOMMENDATIONS
REF
IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESL AND ESR.
driving each differential input
0V TO V
V
Figure 33. Driving the AD7626 from a Differential Analog Source Using ADA4899-1
REF
ADA4899-1
ADA4899-1
VCM
TO 0V
REF
ADA4932-1
–V
+V
–V
+V
S
S
S
S
0.1µF
56pF
56pF
20Ω
20Ω
is
Rev. A | Page 18 of 8
+V
–V
REF
S
S
1
AD8031, AD8032
IN+
IN–
(UNIPOLAR 0V TO 4.096V)
C
10µF
REF
Figure 32. Single-Ended-to-Differential Driver Circuit Using ADA4899-1
2
GND
REF
AD7626
ANALOG INPUT
REFIN
VCM
2.048V
100nF
C
10µF
REF
50Ω
2
U1
ADA4899-1
590Ω
590Ω
U2
ADA4899-1
REF
1
20Ω
20Ω
V+
V–
56pF
AD8031, AD8032
56pF
100nF
IN+
IN–
AD7626
VCM